Internet Engineering Task Force (IETF) G. Karagiannis
Request for Comments: 6627 University of Twente
Category: Informational K. Chan
ISSN: 2070-1721 Consultant
T. Moncaster
University of Cambridge
M. Menth
University of Tuebingen
P. Eardley
B. Briscoe
BT
July 2012
Overview of Pre-Congestion Notification Encoding
Abstract
The objective of Pre-Congestion Notification (PCN) is to protect the
quality of service (QoS) of inelastic flows within a Diffserv domain.
On every link in the PCN-domain, the overall rate of PCN-traffic is
metered, and PCN-packets are appropriately marked when certain
configured rates are exceeded. Egress nodes provide decision points
with information about the PCN-marks of PCN-packets that allows them
to take decisions about whether to admit or block a new flow request,
and to terminate some already admitted flows during serious
pre-congestion.
The PCN working group explored a number of approaches for encoding
this pre-congestion information into the IP header. This document
provides details of those approaches along with an explanation of the
constraints that apply to any solution.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6627.
Karagiannis, et al. Informational [Page 1]RFC 6627 Pre-Congestion Notification Encoding July 2012Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
Karagiannis, et al. Informational [Page 2]RFC 6627 Pre-Congestion Notification Encoding July 2012Table of Contents
1. Introduction ....................................................4
2. General PCN Encoding Requirements ...............................5
2.1. Metering and Marking Algorithms ............................5
2.2. Approaches for PCN-Based Admission Control and Flow
Termination ................................................5
2.2.1. Dual Marking (DM) ...................................5
2.2.2. Single Marking (SM) .................................6
2.2.3. Packet-Specific Dual Marking (PSDM) .................7
2.2.4. Preferential Packet Dropping ........................8
3. Encoding Constraints ............................................9
3.1. Structure of the DS Field ..................................9
3.2. Constraints from the DS Field ..............................9
3.2.1. General Scarcity of DSCPs ...........................9
3.2.2. Handling of the DSCP in Tunneling Rules ............10
3.2.3. Restoration of Original DSCPs at the Egress Node ...10
3.3. Constraints from the ECN Field ............................11
3.3.1. Structure and Use of the ECN Field .................11
3.3.2. Redefinition of the ECN Field ......................12
3.3.3. Handling of the ECN Field in Tunneling Rules .......12